The present invention relates to conductor bars for dynamoelectric machines, and more particularly to a high efficiency conductor with high current capacity.
The conductor of the present invention is particularly suitable for use in air gap windings for dynamoelectric machines of high power density. Advanced types of dynamoelectric machines now under development, such as those having superconducting field windings, for example, utilize air gap windings which operate in very high flux density environments, as compared to the windings of conventional machines. Such windings must be capable of carrying very high currents without excessive heating or losses, while the flux density requires fine stranding of the winding conductors with complete transposition of the strands.
These conditions require a stranded conductor made up of many small strands, and the dimensions of the strands must be approximately the same in both the radial and tangential directions of the machine. This requires round or square strands of very much smaller dimensions than the conductor strands that have been used in conventional dynamoelectric machines, and in order to minimize losses due to circulating currents, the strands must be fully transposed in both the radial and tangential directions. The use of a large number of small diameter strands, while it is necessary for minimizing eddy current losses, results in a relative increase in the amount of insulation in the conductor since each strand must be insulated at least for the expected strand-to-strand voltage. This has the effect of reducing the effective cross-section of copper which tends to increase the copper loss. The amount of insulation must, therefore, be kept to a minimum to provide as great a copper cross-section as possible within the overall dimensional limitations. It is desirable to prevent excessive temperature rise due to the losses in the conductor, which requires provision for circulating water, or other coolant fluid, through the conductor, as by means of a coolant tube incorporated in the conductor bar. These various design requirements cannot be met by any existing type of conductor bar construction used in conventional dynamoelectric machines.